So I've got 2 Gainward 780's in SLI and in some games I get massive FPS drops (so far its LoL and Bf3).

The FPS will be sitting at whatever e.g. 100 fps then drop suddenly to 1-20 FPS and then come back up again. In Bf3 it isn't as bad, but in league of legends my entire screen freezes. I've tried it with SLI on and off, doesn't fix it. Overclocking doesn't seem to be the issue as I've had it at default clock and it still happens.

Ok nothing came up under Perfcap reason. But my clocks were sitting @ 666 mhz core and 400 mhz memory clock during the game and going to full clock when the spikes happened. The driver update definitely made a difference. Still a bit of lag though. Testing out BF3 now.

push the power limit to 120% that should solve the issues.
If that doesn't help cranck the fans to 100% and see if it stops the frequency drops.
make sure you don't have any 2D video running in the background ie: youtube